Photomask blank, photomask, and methods of manufacturing the same

ABSTRACT

A photomask blank is for manufacturing a phase shift mask having a light-transmitting substrate provided with a phase shift portion adapted to give a predetermined phase difference to transmitted exposure light. The phase shift portion is a dug-down part that is dug down from a surface of the light-transmitting substrate to a digging depth adapted to produce the predetermined phase difference with respect to exposure light transmitted through the light-transmitting substrate at a portion where the phase shift portion is not provided. The photomask blank includes, on the digging-side surface of the light-transmitting substrate, an etching mask film that is made of a material being dry-etchable with a chlorine-based gas, but not dry-etchable with a fluorine-based gas, and serves as an etching mask at least until, when forming the dug-down part by dry etching, the dry etching reaches the digging depth. The photomask blank further includes, on a surface of the etching mask film, a light-shielding film that is made of a material mainly containing tantalum and has a thickness so as to be removable during the dry etching for forming the dug-down part of the light-transmitting substrate.

This is a Divisional of Application No. 12/414,198 filed Mar. 30, 2009,claiming priority based on Japanese Patent Application No. 2008-94139,filed on Mar. 31, 2008, the contents of all of which are incorporatedherein by reference in their entirety.

TECHNICAL FIELD

This invention relates to a photomask blank and a photomask for use inmanufacturing semiconductor devices and so on and to methods ofmanufacturing the same.

BACKGROUND ART

Miniaturization of semiconductor devices and so on has the advantage ofachieving improvement in performance and function (high-speed operation,low power consumption, etc.) and reduction in cost and is increasinglyaccelerated. Such miniaturization is supported by the lithographytechnology. A transfer mask is one of key techniques, as well as anexposure apparatus and a resist material.

In recent years, development is made of the technology for a 45 nm to 32nm half-pitch (hp) generation defined in the semiconductor design rule.The half pitch of 45 nm to 32 nm corresponds to ¼ to ⅙ of the wavelengthof 193 nm of ArF excimer laser exposure light (hereinafter referred toas “ArF exposure light”). In particular, in the 45 nm hp generation andbeyond, only the application of the resolution enhancement technology(RET) such as conventional phase shift technique, oblique-incidenceillumination, and pupil filtering, and the optical proximity correction(OPC) has become insufficient. Therefore, the hyper-NA technique(immersion lithography) and the double exposure (double patterning)technique are required.

In the meantime, circuit patterns necessary in the semiconductormanufacture are exposed in sequence onto a semiconductor wafer by aplurality of photomask (reticle) patterns. For example, a reducedprojection exposure apparatus with a predetermined reticle set thereinrepeatedly projects and exposes patterns while sequentially shiftingprojection regions on a semiconductor wafer (step-and-repeat system), orrepeatedly projects and exposes patterns while synchronously scanningthe reticle and a semiconductor wafer with respect to a projectionoptical system (step-and-scan system). By this, a predetermined numberof integrated circuit chip regions are formed in the semiconductorwafer.

A photomask (reticle) has a region formed with a transfer pattern and aperipheral region thereof, i.e. an edge region along four sides in thephotomask (reticle). When exposing the transfer pattern of the photomask(reticle) while sequentially shifting projection regions on asemiconductor wafer, the transfer pattern is exposed and transferredonto the projection regions so that the photomask peripheral regionsoverlap each other for the purpose of increasing the number ofintegrated circuit chips to be formed. In order to prevent exposure of aresist on the wafer due to such overlapping exposure, a light-shieldingband (light-shielder band or light-shielder ring) is formed in theperipheral region of the photomask by mask processing.

The phase shift method is a technique of giving a predetermined phasedifference to exposure light transmitted through a phase shift portion,thereby improving the resolution of a transfer pattern usinginterference of light.

As photomasks improved in resolution by the phase shift method, thereare a substrate dug-down type in which a shifter portion is provided bydigging down a quartz substrate by etching or the like, and a type inwhich a shifter portion is provided by patterning a phase shift filmformed on a substrate.

SUMMARY OF THE INVENTION

As photomasks of the substrate dug-down (carved) type, there are aLevenson-type phase shift mask, an enhancer-type phase shift mask, achromeless phase shift mask, and so on. As chromeless phase shift masks,there are a type in which a light-shielding layer on lines is completelyremoved, and a type in which a light-shielding layer on lines ispatterned (so-called zebra type). A Levenson-type phase shift mask or achromeless phase shift mask of the type in which a light-shielding layerin a transfer region is completely removed is also called an alternativephase shifter which is a phase shift mask of the type in which exposurelight incident on a phase shift portion is transmitted at approximately100%. An enhancer-type phase shift mask is provided with alight-shielding portion, a transmittance control portion (phase shift of360°=)0°, and a 180° shift portion formed by digging down a glass. Inany type, it is necessary to form a light-shielding band in an edgeregion (peripheral region) along four sides in the photomask (reticle).

As a photomask blank for manufacturing such a chromeless phase shiftmask, there is known one in which a CrO/Cr light-shielding filmcomprising a light-shielding layer made of Cr and a low reflection layermade of CrO stacked together is formed on a transparent substrate andhas a total thickness of 70 to 100 nm (see, e.g. JP-A-2007-241136(Patent Document 1), paragraph [0005]). In manufacturing processes ofthe chromeless phase shift mask, the substrate is dug down using alight-shielding film pattern as an etching mask and, after removing aresist pattern used for forming the light-shielding film pattern, aresist is applied again and subjected to exposure and development so asto protect a portion where the light-shielding film is to remain, andthen the light-shielding film at an unnecessary portion is removed byetching, thereby obtaining the photomask having a light-shielding bandin the substrate peripheral region and a light-shielding pattern in thetransfer region according to need. That is, the light-shielding film hasboth a function as an etching mask (also called a hard mask) and afunction as a layer for forming the light-shielding band and thelight-shielding pattern (function of ensuring the light-shieldingperformance).

Generally, in order to improve the CD performance of a photomask, it iseffective to reduce the thickness of a light-shielding film and thethickness of a resist for forming the light-shielding film. However, ifthe thickness of the light-shielding film is reduced, the CD value(optical density) decreases. In the case of the above CrO/Crlight-shielding film, the total thickness of about 60 nm is required atminimum for achieving OD=3 which is generally required, and thus, it isdifficult to largely reduce the thickness thereof. If the thickness ofthe light-shielding film cannot be reduced, it is also not possible toreduce the thickness of the resist due to the etching selectivitybetween the light-shielding film and the resist. Thus, a largeimprovement in CD cannot be expected.

As a measure for this, Patent Document 1 proposes a method. This methodis intended to satisfy the above requirement by forming alight-shielding film and an etching mask film of different materials.

In the method of Patent Document 1, the layer structure is, for example,substrate/Cr-based second etching mask film/MoSi-based light-shieldingfilm/Cr-based first etching mask film (also serving as an antireflectionfilm) and thus a Cr-based material is used as the first etching maskfilm at the outermost surface farthest from the substrate (see PatentDocument 1, paragraph [0038] etc.). By this, a resist film to be appliedon the upper surface of the first etching mask film is only required, atminimum, to transfer a pattern to the first etching mask film and thus areduction in thickness of the resist film can be achieved to somedegree. However, the first etching mask film of the Cr-based materialshould be dry-etched with a mixed gas of chlorine and oxygen and thusthe etching selectivity to the resist is low (etching amount of theresist is large). Therefore, there is a problem that it is difficult tolargely reduce the thickness of the resist film (to realize a resistfilm thickness of 200 nm or less and further 150 nm) and the CD accuracycannot be set to be sufficient, and therefore, it is difficult torealize high accuracy with a mask pattern resolution of about 65 nm orless and further 50 nm or less.

Further, in the method of Patent Document 1, the layer structure is suchthat the two Cr-based etching mask films are provided above and belowthe MoSi-based light-shielding film, and therefore, there is a problemthat the processes of manufacturing the photomask blank becomecomplicated.

Further, there is also a problem that the manufacturing processes becomecomplicated because the number of layers is large. For example, in thismethod, it is necessary to use the photomask blank having the layerstructure of substrate/Cr-based second etching mask film/MoSi-basedlight-shielding film/Cr-based first etching mask film (also serving asan antireflection film) (see Patent Document 1, paragraph [0038] etc.),and therefore, there is a problem that the manufacturing processesbecome complicated due to a large number of layers.

The above description also applies to the case of using a photomaskblank having a layer structure of, for example, Substrate/MoSi-basedphase shift film/Cr-based second etching mask film/MoSi-basedlight-shielding film/Cr-based first etching mask film (also serving asan antireflection film) (see JP-A-2007-241065 (Patent Document 2),paragraph [0174] etc.) and thus there is a problem that themanufacturing processes become complicated due to a large number oflayers.

Further, the light-shielding film made of a MoSi-based material has lowresistance to chemical cleaning (particularly to ammonia-hydrogenperoxide mixture cleaning) and also has low resistance to hot watercleaning (e.g. cleaning with hot water of 90° C.) and, therefore, thereis a problem in cleaning after manufacturing a photomask.

It is an object of this invention to provide photomask blank andphotomask manufacturing methods that can simplify manufacturingprocesses without sacrificing processing accuracy.

It is an object of this invention to provide photomask blank andphotomask manufacturing methods that can reduce the number of layerswithout sacrificing processing accuracy.

It is an object of this invention to provide methods of manufacturing aphotomask blank and a photomask that can achieve, with a small number oflayers, the following four subjects (1) to (4) that are closely relatedto each other:

(1) To realize a resolution of about 65 nm or less and further 50 nm orless with respect to a pattern on a photomask;

(2) To ensure an optical density OD>3 of a light-shielding portioncomprising a light-shielding film or a light-shielding film and upperand lower layers thereof;

(3) To prevent collapse of a resist pattern by realizing a ratio of theheight (thickness) of the resist pattern to the width thereof beingthree or less (realizing a resist film thickness of 200 nm or less andfurther 150 nm) due to a reduction in resist film thickness;

(4) To ensure the conductivity of a film coated with an EB resist; and

(5) To improve the resistance of a photomask, manufactured from aphotomask blank, to chemical cleaning and hot water cleaning.

The present inventor has found that the above objects can be achievednot by using a Cr-based thin film as an etching mask film to be directlytransferred with a resist film pattern like in the method described inPatent Document 1 wherein the layer structure is, for example,substrate/Cr-based second etching mask film/MoSi-based light-shieldingfilm/Cr-based first etching mask film (also serving as an antireflectionfilm), but by using a light-shielding film mainly containing Ta anddirectly transferring a resist film pattern onto the light-shieldingfilm, and has completed this invention.

In this invention, for example, in a halftone or glass dug-down typephase shift mask, use is made of a photomask blank having alight-shielding film in which a thin film layer mainly containing Cr, alight-shielding layer mainly containing Ta, and an antireflection layermainly containing Ta oxide are stacked together in this order.

The thin film layer mainly containing Cr is not substantially dry-etchedwith a fluorine-based gas and thus serves as an etching mask (alsocalled a hard mask) when etching a halftone phase shift film or a glasssubstrate using a fluorine-based gas. The antireflection layer mainlycontaining Ta oxide is not substantially dry-etched with a mixed gas ofa chlorine-based gas and an oxygen gas and, further, Ta is a material tobe easily oxidized and thus is oxidized and not substantially dry-etchedwith a mixed gas of chlorine and oxygen. Therefore, the antireflectionlayer mainly containing Ta oxide serves as a hard mask when etching thethin film layer mainly containing Cr with a mixed gas of achlorine-based gas and an oxygen gas. A resist film has higher etchingresistance to a fluorine-based gas used in dry-etching a Ta-basedlight-shielding film than to a mixed gas of a chlorine-based gas and anoxygen gas. Therefore, it is possible to achieve a reduction inthickness of the resist film and further to enhance the processingaccuracy when transferring a pattern onto the Ta-based light-shieldingfilm.

The light-shielding layer mainly containing Ta and the antireflectionlayer mainly containing Ta oxide are removed during etching with afluorine-based gas for forming a phase shift pattern and, thus, only thethin film layer mainly containing Cr remains after the formation of thephase shift pattern. Therefore, it is also possible to simplify themanufacturing processes for manufacturing a photomask.

The effects of this invention will be shown below.

(1) A Ta-based film is used as a hard mask in etching of a Cr-basedfilm, which enables a reduction in resist film thickness necessary forfine pattern formation. Simultaneously, sufficient light-shieldingperformance (OD) is maintained.

(2) The Ta-based film is removed during etching with a fluorine-basedgas for forming a phase shift pattern and the remaining Cr-based filmcan be removed by dry etching with a mixed gas of a chlorine-based gasand an oxygen gas or by a chemical solution such as ceric ammoniumnitrate without damaging the phase shift pattern.

(3) By forming an antireflection layer as a Ta oxide layer, it ispossible to improve the resistance to hot water and alkali, whichotherwise becomes a problem with an antireflection film of MoSiON or thelike.

This invention has the following aspects.

(First Aspect)

A photomask blank for manufacturing a phase shift mask having alight-transmitting substrate provided with a phase shift portion adaptedto give a predetermined phase difference to transmitted exposure light,

wherein the phase shift portion is a dug-down part that is dug down froma surface of the light-transmitting substrate to a digging depth adaptedto produce the predetermined phase difference with respect to exposurelight transmitted through the light-transmitting substrate at a portionwhere the phase shift portion is not provided, and

the photomask blank comprises:

an etching mask film, on a digging-side surface of thelight-transmitting substrate, that is made of a material beingdry-etchable with a chlorine-based gas, but not dry-etchable with afluorine-based gas, and serves as an etching mask at least until, whenforming the dug-down part by dry etching, the dry etching reaches thedigging depth; and

a light-shielding film, on a surface of the etching mask film, that ismade of a material mainly containing tantalum and has a thickness so asto be removable during the dry etching for forming the dug-down part ofthe light-transmitting substrate.

(Second Aspect)

A photomask blank for manufacturing a phase shift mask having alight-transmitting substrate provided with a phase shift portion adaptedto give a predetermined phase difference to transmitted exposure light,

wherein the phase shift portion is a phase shift film adapted to give apredetermined phase change amount to the transmitted exposure light, and

the photomask blank comprises:

an etching mask film, on a surface of the phase shift film, that is madeof a material being dry-etchable with a chlorine-based gas, but notdry-etchable with a fluorine-based gas, and serves as an etching mask atleast until a transfer pattern is formed in the phase shift film by dryetching; and

a light-shielding film, on a surface of the etching mask film, that ismade of a material mainly containing tantalum and has a thickness so asto be removable during the dry etching for forming the transfer patternin the phase shift film.

(Third Aspect)

A photomask blank according to first or second aspect, wherein thelight-shielding film comprises:

a light-shielding layer mainly containing tantalum nitride; and

an antireflection layer stacked on an upper surface of thelight-shielding layer and mainly containing tantalum oxide.

(Fourth Aspect)

A photomask blank according to any one of first to third aspects,wherein the thickness of the light-shielding film is 15 nm to 50 nm.

(Fifth Aspect)

A photomask blank according to any one of first to fourth aspects,wherein the etching mask film is made of a material mainly containingone of chromium, chromium nitride, chromium oxide, chromium oxynitride,and chromium oxycarbonitride.

(Sixth Aspect)

A photomask blank according to any one of first to fifth aspects,wherein the etching mask film has a thickness of 5 nm to 40 nm.

(Seventh Aspect)

A photomask blank according to any one of second to sixth aspects,wherein the phase shift film is made of a material mainly containing oneof molybdenum silicide, molybdenum silicide nitride, molybdenum silicideoxide, and molybdenum silicide oxynitride.

(Eighth Aspect)

A photomask blank according to claim any one of second to sixth aspects,wherein the phase shift film comprises a phase adjusting layer made of amaterial mainly containing silicon oxide or silicon oxynitride and atransmittance adjusting layer made of a material mainly containingtantalum or a tantalum-hafnium alloy.

(Ninth Aspect)

A photomask manufactured using the photomask blank according to any oneof first to eighth aspects.

According to this invention, it is possible to provide photomask blankand photomask manufacturing methods that can simplify manufacturingprocesses without sacrificing processing accuracy.

According to this invention, it is possible to provide photomask blankand photomask manufacturing methods that can reduce the number of layerswithout sacrificing processing accuracy.

According to this invention, it is possible to provide methods ofmanufacturing a photomask blank and a photomask that can achieve, with asmall number of layers, the following four subjects (1) to (4) that areclosely related to each other:

(1) To realize a resolution of about 65 nm or less and further 50 nm orless with respect to a pattern on a photomask;

(2) To ensure an optical density OD>3 of a light-shielding portioncomprising a light-shielding film or a light-shielding film and upperand lower layers thereof;

(3) To prevent collapse of a resist pattern by realizing a ratio of theheight (thickness) of the resist pattern to the width thereof beingthree or less (realizing a resist film thickness of 200 nm or less andfurther 150 nm) due to a reduction in resist film thickness;

(4) To ensure the conductivity of a film coated with an EB resist; and

(5) To improve the resistance of a photomask, manufactured from aphotomask blank, to chemical cleaning and hot water cleaning.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an exemplary sectional view showing one example of a photomaskblank according to a first embodiment of this invention;

FIG. 2 is an exemplary sectional view showing one example of a photomaskblank according to a second or third embodiment of this invention;

FIG. 3 is an exemplary sectional view showing one example of a photomaskblank according to a fourth embodiment of this invention;

FIGS. 4A to 4I are exemplary sectional views for explainingmanufacturing processes of a photomask according to Example 1 of thisinvention;

FIGS. 5A to 5J are exemplary sectional views for explainingmanufacturing processes of a photomask according to Example 2 of thisinvention;

FIGS. 6A to 6I are exemplary sectional views for explainingmanufacturing processes of a photomask according to Example 3 of thisinvention;

FIGS. 7A to 7J are exemplary sectional views for explainingmanufacturing processes of a photomask according to Example 4 of thisinvention;

FIGS. 8A to 8J are exemplary sectional views for explainingmanufacturing processes of a photomask according to Example 5 of thisinvention; and

FIGS. 9A to 9K are exemplary sectional views for explainingmanufacturing processes of a photomask according to Example 6 of thisinvention.

DETAILED DESCRIPTION OF THE INVENTION

Hereinbelow, this invention will be described in detail.

According to this invention of the first aspect, there is provided aphotomask blank for manufacturing a phase shift mask having alight-transmitting substrate provided with a phase shift portion adaptedto give a predetermined phase difference to transmitted exposure light,

wherein the phase shift portion is a dug-down part that is dug down froma surface of the light-transmitting substrate to a digging depth adaptedto produce the predetermined phase difference with respect to exposurelight transmitted through the light-transmitting substrate at a portionwhere the phase shift portion is not provided, and

the photomask blank comprises:

an etching mask film, on a digging-side surface of thelight-transmitting substrate, that is made of a material beingdry-etchable with a chlorine-based gas, but not dry-etchable with afluorine-based gas, and serves as an etching mask at least until, whenforming the dug-down part by dry etching, the dry etching reaches thedigging depth; and

a light-shielding film, on a surface of the etching mask film, that ismade of a material mainly containing tantalum and has a thickness so asto be removable during the dry etching for forming the dug-down part ofthe light-transmitting substrate.

In this invention, the material not dry-etchable with the fluorine-basedgas also includes a material that is physically etched, but serves as anetching mask until the dug-down part reaches the digging depth adaptedto produce the predetermined phase difference while the dry etching isperformed using the fluorine-based gas for forming the dug-down part onthe light-transmitting substrate.

According to this aspect, the light-shielding film made of the materialmainly containing tantalum and having the thickness so as to beremovable during the dry etching for forming the dug-down part of thelight-transmitting substrate is removed during the dry etching forforming the dug-down part of the light-transmitting substrate.Therefore, it is possible to simplify the manufacturing processes.

Further, by the use of the tantalum-based light-shielding film, it ispossible to achieve a reduction in thickness of a resist to be formedthereon, which is necessary for fine pattern formation. This is becausethe resist is highly resistant to an etching gas for the tantalum-basedlight-shielding film.

Moreover, a photomask manufactured from this photomask blank can behighly resistant to chemical cleaning and hot water cleaning. This isbecause the tantalum-based light-shielding film is highly resistant tochemical cleaning (particularly to ammonia-hydrogen peroxide mixturecleaning) and hot water cleaning.

FIG. 1 shows one example of a photomask blank according to a firstembodiment of this invention.

The photomask blank shown in FIG. 1 is used for manufacturing a phaseshift mask of the substrate dug-down type.

This photomask blank comprises an etching mask film 10, a Ta-basedlight-shielding film 20 composed of a Ta-based light-shielding layer 21and a Ta-based antireflection layer 22, and a resist film 50 which areformed in this order on a surface of a transparent substrate 1.

FIG. 4I shows one example of a phase shift mask of the substratedug-down type.

According to this invention of the second aspect, there is provided aphotomask blank for manufacturing a phase shift mask having alight-transmitting substrate provided with a phase shift portion adaptedto give a predetermined phase difference to transmitted exposure light,

wherein the phase shift portion is a phase shift film adapted to give apredetermined phase change amount to the transmitted exposure light, and

the photomask blank comprises:

an etching mask film, on a surface of the phase shift film, that is madeof a material being dry-etchable with a chlorine-based gas, but notdry-etchable with a fluorine-based gas, and serves as an etching mask atleast until a transfer pattern is formed in the phase shift film by dryetching; and

a light-shielding film, on a surface of the etching mask film, that ismade of a material mainly containing tantalum and has a thickness so asto be removable during the dry etching for forming the transfer patternin the phase shift film.

According to this aspect, the light-shielding film made of the materialmainly containing tantalum and having the thickness so as to beremovable during the dry etching for forming the transfer pattern in thephase shift film is removed during the dry etching for forming thetransfer pattern in the phase shift film. Therefore, it is possible tosimplify the manufacturing processes.

Further, by the use of the tantalum-based light-shielding film, it ispossible to achieve a reduction in thickness of a resist to be formedthereon, which is necessary for fine pattern formation.

Moreover, by the use of the tantalum-based light-shielding film, aphotomask manufactured from this photomask blank can be highly resistantto chemical cleaning and hot water cleaning.

FIG. 2 shows one example of a photomask blank according to a secondembodiment of this invention.

The photomask blank shown in FIG. 2 is used for manufacturing a phaseshift mask of the type in which a substrate is not basically dug downand a phase shift portion is formed by a halftone phase shift film.

This photomask blank comprises a halftone phase shift film 30, anetching mask film 10, a Ta-based light-shielding film 20 composed of aTa-based light-shielding layer 21 and a Ta-based antireflection layer22, and a resist film 50 which are formed in this order on a surface ofa transparent substrate 1.

FIG. 6I shows one example of a phase shift mask of this type. As shownin FIG. 6I, this type of phase shift mask has a halftone phase shiftfilm pattern 30 a on a substrate 1.

One example of a photomask blank according to a third embodiment of thisinvention will be described with reference to FIG. 2 which was used fordescribing the second embodiment of this invention.

The photomask blank according to the third embodiment is used formanufacturing a phase shift mask of the type in which ahigh-transmittance phase shift portion is formed by providing a halftonephase shift film and further by digging down a substrate.

This photomask blank comprises a halftone phase shift film 30, anetching mask film 10, a Ta-based light-shielding film 20 composed of aTa-based light-shielding layer 21 and a Ta-based antireflection layer22, and a resist film 50 which are formed in this order on a surface ofa transparent substrate 1.

FIG. 8J shows one example of a phase shift mask of this type. As shownin FIG. 8J, this type of phase shift mask has a phase shift portionconfigured by forming a thin halftone phase shift film pattern 30 a on adug-down part 1 a of a substrate. In the case of the single-layer phaseshift film shown in the second embodiment, a considerably largethickness is required for giving a predetermined phase difference (phaseshift amount) to exposure light and simultaneously controlling thetransmittance to a predetermined value for the exposure light. In viewof this, the photomask blank according to the third embodiment realizeshigh transmittance for exposure light by reducing the thickness of thesingle-layer phase shift film and further realizes that a predeterminedphase difference is given to the exposure light by providing thedug-down part la, having a thickness corresponding to a phase shiftamount lessened by reducing the film thickness, at a substrate exposedportion where the halftone phase shift film pattern 30 a is not formed.

FIG. 3 shows one example of a photomask blank according to a fourthembodiment of this invention.

The photomask blank shown in FIG. 3 is used for manufacturing a phaseshift mask of the type in which a substrate is not dug down and ahigh-transmittance phase shift portion is formed by providing ahigh-transmittance halftone phase shift film. In order to obtain hightransmittance, the halftone phase shift film comprises two layers, i.e.a phase control layer and a transmittance control layer.

This photomask blank comprises a halftone phase shift film 30 composedof a phase control layer 32 and a transmittance control layer 31, anetching mask film 10, a Ta-based light-shielding film 20 composed of aTa-based light-shielding layer 21 and a Ta-based antireflection layer22, and a resist film 50 which are formed in this order on a surface ofa transparent substrate 1.

FIG. 9K shows one example of a phase shift mask of this type. As shownin FIG. 9K, this type of phase shift mask has, on a substrate 1, apattern 30 a of a halftone phase shift film 30 composed of a phasecontrol layer 32 and a transmittance control layer 31.

In this invention, as the material mainly containing tantalum, use canbe made of a tantalum-based material, for example, tantalum alone or amaterial containing tantalum and at least one kind of elements such asoxygen, nitrogen, carbon, hydrogen, boron, and silicon(tantalum-containing material).

In this invention, as a film structure of the light-shielding film madeof the material mainly containing tantalum, a multilayer structure madeof the above film materials is often employed, but a single-layerstructure may alternatively be employed. In the case of the multilayerstructure, it is possible to use a multilayer structure with layers ofstepwise different compositions or a film structure having acontinuously varying composition.

In this invention, it is necessary that the etching mask film be made ofthe material being dry-etchable with the chlorine-based gas (including amixed gas of a chlorine-based gas and an oxygen gas), but notdry-etchable with the fluorine-based gas and serve as an etching mask atleast until the transfer pattern is formed in the phase shift film bythe dry etching using the fluorine-based gas. As such an etching maskfilm, there can be cited a film made of chromium, hafnium, zirconium, analloy containing such an element, or a material containing such anelement or alloy (e.g. a material containing such an element or alloyand at least one of oxygen, nitrogen, silicon, and carbon).

On the other hand, use may be made, as the etching mask film, of achromium-based material, a hafnium-based material, or a zirconium-basedmaterial etchable with the chlorine-based gas (including a mixed gas ofa chlorine-based gas and an oxygen gas) and containing at least one kindof elements such as molybdenum, titanium, vanadium, and silicon foradjusting the fine structure and durability.

In this invention, it is preferable that the etching mask film can bestripped by dry etching or wet etching without damaging the substrateand other layers.

In this invention, the etching selectivity of the etching mask film tothe substrate or other layer (etching rate of the etching maskfilm/etching rate of the substrate or other layer) is preferably 1/5 orless.

In this invention, the phase shift film is preferably made of a materialthat is substantially dry-etchable with the fluorine-based gas, but notsubstantially dry-etchable with the chlorine-based gas.

In this invention, use can be made, as the phase shift film, of, forexample, a silicon-containing film containing silicon. As thesilicon-containing film, there can be cited a silicon film, a metalsilicide film containing silicon and a metal such as chromium, tantalum,molybdenum, titanium, hafnium, or tungsten, or a film containing atleast one of oxygen, nitrogen, and carbon in a silicon film or a metalsilicide film.

In this invention, use can be made, as the phase shift film, of, forexample, a film mainly containing transition metal silicide oxide,transition metal silicide nitride, transition metal silicide oxynitride,transition metal silicide oxycarbide, transition metal silicide nitridecarbide, or transition metal silicide oxycarbonitride. As the phaseshift film, use can be made of, for example, a halftone film such as amolybdenum-based (MoSiON, MoSiN, MoSiO, or the like) film, atungsten-based (WSiON, WSiN, WSiO, or the like) film, or a silicon-based(SiN, SiON, or the like) film.

In this invention, use can be made, as the phase shift film, of, forexample, a halftone film composed of two layers, i.e. a phase adjustinglayer for mainly controlling the phase of exposure light and atransmittance adjusting layer for mainly controlling the transmittanceof exposure light.

In this invention, use can be made, as the phase shift film, of, forexample, a halftone film composed of two layers, i.e. a phase adjustinglayer for mainly controlling the phase of exposure light and atransmittance adjusting layer for mainly controlling the transmittanceof exposure light (see JP-A-2003-322947). Herein, as a material of thetransmittance adjusting layer, use can be made of a material containingone kind or two or more kinds selected from metals and silicon, or anoxide, nitride, oxynitride, carbide, or the like thereof. Specifically,there can be cited a material containing one kind or two or more kindsselected from aluminum, titanium, vanadium, chromium, zirconium,niobium, molybdenum, lanthanum, tantalum, tungsten, silicon, andhafnium, or an oxide, nitride, oxynitride, carbide, or the like thereof.As the phase adjusting layer, it is preferable to use a silicon-basedthin film made of silicon oxide, silicon nitride, silicon oxynitride, orthe like because relatively high transmittance can be easily obtainedfor exposure light in the ultraviolet region.

According to this invention of the third aspect, the light-shieldingfilm preferably comprises:

a light-shielding layer mainly containing tantalum nitride; and

an antireflection layer stacked on an upper surface of thelight-shielding layer and mainly containing tantalum oxide.

According to this aspect, the tantalum-based light-shielding film can beformed by the TaN-based light-shielding layer made of a materialdry-etchable with a chlorine-based gas containing no oxygen (including achlorine-based gas containing substantially no oxygen, i.e. achlorine-based gas containing oxygen in an amount not affecting a resistfilm and so on during dry etching) and the TaO-based front-surfaceantireflection layer formed on the upper surface of the TaN-basedlight-shielding layer and made of a material that is not substantiallydry-etchable with a chlorine-based gas, but dry-etchable with afluorine-based gas. When dry-etching the tantalum-based light-shieldingfilm with the fluorine-based gas using as a mask a resist pattern formedon the TaO-based antireflection layer in contact therewith, it issufficient to etch only the thin TaO-based antireflection layer, andtherefore, the resist film thickness can be reduced as compared with thecase where the entire tantalum-based light-shielding film (TaN-basedlight-shielding layer/TaO-based antireflection layer) is dry-etchedusing a fluorine-based gas and thus it becomes possible to achieveimprovement in processing accuracy of the TaO-based antireflectionlayer.

Further, when dry-etching the TaN-based light-shielding layer with thechlorine-based gas containing substantially no oxygen using a TaO-basedantireflection layer pattern as a mask, the TaO-based antireflectionlayer pattern is not dry-etched with the chlorine-based gas, i.e. itserves well as an etching mask. Therefore, it becomes possible toachieve improvement in processing accuracy of the TaN-basedlight-shielding layer.

Further, a pattern of the tantalum-based light-shielding film (TaN-basedlight-shielding layer/TaO-based antireflection layer) serves well as anetching mask when etching the etching mask film (e.g. a Cr-based thinfilm layer), formed under the tantalum-based light-shielding film incontact therewith, using a chlorine-based gas (e.g. Cl₂+O₂). Therefore,it becomes possible to achieve improvement in processing accuracy of theetching mask film (e.g. the Cr-based thin film layer).

In view of the above, this invention can provide methods ofmanufacturing a photomask blank and a photomask characterized in that amain light-shielding layer and an antireflection layer formed thereonboth serve as etching mask layers for an underlayer, i.e. characterizedby having a light-shielding film with a structure (configuration) inwhich two or more etching mask layers are stacked.

In view of the above, this invention can provide methods ofmanufacturing a photomask blank and a photomask characterized in thatthree layers, i.e. an etching mask film, a main light-shielding layerformed thereon, and an antireflection layer formed thereon, all serve asetching mask layers for an underlayer, i.e. characterized by having aprocessing and light-shielding film with a structure (configuration) inwhich three or more etching mask layers are stacked.

In addition to the above, according to Configuration 3, by forming theantireflection layer as a Ta oxide layer, it is possible to improve theresistance to hot water and alkali, which otherwise becomes a problemwith an antireflection film of MoSiON or the like.

In addition to the above, according to Configuration 3, by providing theTa-based light-shielding layer being a metal layer, the conductivity canbe ensured so as to prevent charge-up during electron beam lithographyon an electron beam resist formed in contact with the antireflectionlayer.

In this invention, the sheet resistance of the substrate formed with theantireflection layer is preferably 500 Ω/square or less.

According to this invention of the fourth aspect, the thickness of thelight-shielding film is preferably 15 nm to 50 nm.

With respect to the upper limit, it is for providing a film thicknessthat enables removal of the tantalum-based light-shielding film (e.g.TaN-based light-shielding layer/TaO-based antireflection layer) duringthe dry etching using the fluorine-based gas for forming the phase shiftpattern.

With respect to the lower limit, it is for ensuring the optical densityand the function as a charge-up preventing layer.

According to this invention of the fifth aspect, the etching mask filmis preferably made of a material mainly containing one of chromium,chromium nitride, chromium oxide, chromium oxynitride, and chromiumoxycarbonitride.

According to this aspect, the etching mask film can be reduced inthickness. Further, it is excellent in processing accuracy. In addition,the etching selectivity of the etching mask film to the upper and lowerlayers formed in contact therewith is high and, therefore, the etchingmask film that becomes unnecessary can be removed without damaging thesubstrate and other layers.

In this invention, as the etching mask film, use can be made of achromium-based material, for example, chromium alone or a materialcontaining chromium and at least one kind of elements such as oxygen,nitrogen, carbon, and hydrogen (Cr-containing material).

As a film structure of the etching mask film, a single-layer structuremade of the above film material is often employed, but a multilayerstructure may alternatively be employed. In the case of the multilayerstructure, it is possible to use a multilayer structure with layers ofstepwise different compositions or a film structure having acontinuously varying composition.

As the material of the etching mask film, chromium oxycarbonitride(CrOCN) is preferable among them in terms of stress controllability(low-stress film can be formed).

According to this invention of the sixth aspect, the etching mask filmpreferably has a thickness of 5 nm to 40 nm.

According to this aspect, the etching mask film is excellent inprocessing accuracy and serves as an etching mask for the phase shiftfilm.

According to this invention of the seventh aspect, the phase shift filmis preferably made of a material mainly containing one of molybdenumsilicide, molybdenum silicide nitride, molybdenum silicide oxide, andmolybdenum silicide oxynitride.

According to this configuration, there is obtained a halftone phaseshift mask having a transmittance of, for example, about 3% to 20%forArF exposure light.

According to this invention of the eighth aspect, the phase shift filmpreferably comprises a phase adjusting layer made of a material mainlycontaining silicon oxide or silicon oxynitride and a transmittanceadjusting layer made of a material mainly containing tantalum or atantalum-hafnium alloy.

According to this configuration, it becomes possible to obtain ahigh-transmittance halftone phase shift mask, for example, having atransmittance of 20% or more for ArF exposure light without digging downa substrate.

According to this invention of the ninth aspect, a photomask ismanufactured using the photomask blank according to the aforementionedaspects.

According to this aspect, there is obtained a photomask having the sameoperation and effect as those of any of aspects 1 to 8 described above.

According to this invention, there is provided a photomask manufacturingmethod, comprising the steps of:

dry-etching the light-shielding film using a resist film pattern as amask, thereby forming a light-shielding film pattern;

dry-etching the etching mask film using the light-shielding film patternas a mask, thereby forming an etching mask film pattern; and

dry-etching the light-transmitting substrate using the etching mask filmpattern as a mask, thereby forming a dug-down part that is dug down froma surface of the light-transmitting substrate to a digging depth adaptedto produce a predetermined phase difference.

According to this method, a photomask having the same operation andeffect as those of any of the aforementioned aspects 1 to 8 is obtainedwith high manufacturing process efficiency.

According to this invention, there is provided another photomaskmanufacturing method, comprising the steps of:

dry-etching the light-shielding film using a resist film pattern as amask, thereby forming a light-shielding film pattern;

dry-etching the etching mask film using the light-shielding film patternas a mask, thereby forming an etching mask film pattern; and

dry-etching the phase shift film using the etching mask film pattern asa mask, thereby forming a phase shift film pattern.

According to this method, a photomask having the same operation andeffect as those of any of the aforementioned aspects 1 to 8 is obtainedwith high manufacturing process efficiency.

In this invention, for dry-etching a chromium-based thin film, it ispreferable to use a dry etching gas in the form of a mixed gascontaining a chlorine-based gas and an oxygen gas. This is because if achromium-based thin film made of a material containing chromium and anelement such as oxygen or nitrogen is dry-etched using the above dryetching gas, it is possible to increase the dry etching rate and thus toshorten the dry etching time so that an etching mask film pattern withan excellent sectional shape can be formed. As the chlorine-based gasfor use in the dry etching, there can be cited, for example, Cl₂, SiCl₄,HCl, CCl₄, CHCl₃, or the like.

In this invention, for dry-etching a substrate to form a dug-down partor dry-etching a silicon-containing film containing silicon or a metalsilicide-based thin film, use can be made of, for example, afluorine-based gas such as SF₆, CF₄, C₂F₆, or CHF₃, a mixed gas of sucha fluorine-based gas and He, H₂, N₂, Ar, C₂H₄, O₂ or the like, achlorine-based gas such as Cl₂ or CH₂Cl₂, or a mixed gas of such achlorine-based gas and He, H₂, N₂, Ar, C₂H₄, or the like.

In this invention, the resist is preferably a chemically amplifiedresist. This is because it is suitable for high-accuracy processing.

This invention is applied to photomask blanks of the generation aimingat a resist film thickness of 200 nm or less and further at a resistfilm thickness of 150 nm.

In this invention, the resist is preferably a resist for electron beamlithography. This is because it is suitable for high-accuracyprocessing.

This invention is applied to a photomask blank for electron beamlithography, wherein a resist pattern is formed by electron beamlithography.

In this invention, as a substrate, there can be cited a synthetic quartzsubstrate, a CaF₂ substrate, a soda-lime glass substrate, an alkali-freeglass substrate, a low thermal expansion glass substrate, analuminosilicate glass substrate, or the like.

In this invention, photomask blanks include the above various phaseshift mask blanks and resist-coated mask blanks.

In this invention, photomasks include the above various phase shiftmasks. A reticle is included in the photomasks. The phase shift masksinclude a phase shift mask in which a phase shift portion is formed bydigging down a substrate.

Hereinbelow, Examples of this invention and Comparative Examples thereofwill be shown. In each Example, films such as a light-shielding film, anetching mask film, and a phase shift film were formed by a sputteringmethod as a film forming method using a DC magnetron sputteringapparatus as a sputtering apparatus. However, for carrying out thisinvention, there is no particular limitation to such a film formingmethod and film forming apparatus and use may be made of another type ofsputtering apparatus such as an RF magnetron sputtering apparatus.

EXAMPLE 1

Example 1 relates to a method of manufacturing a photomask blank for usein manufacturing a phase shift mask of the type having a phase shiftportion configured by forming a dug-down part on a substrate and furtherrelates to a method of manufacturing the photomask.

[Manufacture of Photomask Blank]

Referring to FIGS. 4A to 4I, description will be given of photomaskblank and photomask manufacturing methods according to Example 1 of thisinvention.

First, a substrate made of quartz was mirror-polished and then cleaned,thereby obtaining a light-transmitting substrate 1 of 6 inches×6inches×0.25 inches (FIG. 4A).

Then, using a DC magnetron sputtering apparatus, an etching mask film 10was formed on the light-transmitting substrate 1 (FIG. 4A).Specifically, using a chromium target, CrOCN was formed to a thicknessof 20 nm under the conditions of introducing gases and flow rates ofAr=18 sccm, CO₂=18 sccm, N₂=10 sccm and a sputtering power of 1.7 kW. Inthis event, the film stress of the CrOCN film was adjusted to be assmall as possible (preferably, substantially zero).

Then, the substrate 1 formed with the etching mask film 10 wasintroduced into a DC magnetron sputtering apparatus. After the inside ofthe sputtering apparatus was evacuated to 2×10⁻⁵ (Pa) or less, a mixedgas of Xe and N₂ was introduced into the sputtering apparatus. In thisevent, the flow rate of Xe and the flow rate of N₂ were adjusted to 12.7sccm and 10 sccm, respectively. Ta was used as a sputtering target.After the gas flow rates were stabilized, the power of a DC power supplywas set to 1.5 kW, thereby forming a tantalum nitride (TaN) layer 21having a thickness of 24 nm on the etching mask film 10 (FIG. 4A).

Then, while the substrate 1 formed with the tantalum nitride (TaN) layer21 was maintained in the sputtering apparatus, a mixed gas containing anAr gas at a flow rate of 90 sccm and an O₂ gas at a flow rate of 34.7sccm was introduced into the sputtering apparatus and then the power ofthe DC power supply was set to 0.7 kW, thereby stacking a tantalum oxide(TaO) layer 22 having a thickness of 10 nm on the tantalum nitride (TaN)layer 21 (FIG. 4A).

In the manner described above, there was formed a tantalum-basedlight-shielding film 20 comprising the tantalum nitride (TaN) layer 21and the tantalum oxide (TaO) layer 22 stacked together.

The reflectance (front-surface reflectance) of a surface, remote fromthe substrate 1, of the light-shielding film 20 thus formed was 25.7%for ArF exposure light (wavelength: 193 nm). Further, the transmittancefor ArF exposure light was 0.1%. AES (Auger electron spectroscopy)analysis was performed, wherein the N content of the tantalum nitride(TaN) layer 21 was 23at % and the O content of the tantalum oxide (TaO)layer 22 was 65at %.

The sheet resistance was measured for the sample at the stage where thetantalum oxide (TaO) layer 22 was formed, and it was 85 Ω/square.

[Manufacture of Photomask]

As shown in FIG. 4A, using a photomask blank thus manufactured, achemically amplified positive resist 50 for electron beam lithography(exposure) (FEP171: manufactured by FUJIFILM Electronic Materials Co.,Ltd.) was applied to a thickness of 150 nm on the tantalum oxide (TaO)layer 22 by a spin-coating method.

Then, using an electron beam lithography apparatus, pattern writing wasperformed on the resist film 50 and, thereafter, development was carriedout using a predetermined developer, thereby forming a resist pattern 50a (FIG. 4B).

Then, using the resist pattern 50 a as a mask, the tantalum-based film20 having the TaN and TaO layers stacked together was dry-etched,thereby forming a tantalum-based film pattern 20 a (tantalum nitride(TaN) layer pattern 21 a/tantalum oxide (TaO) layer pattern 22 a) (FIG.4C). In this event, CHF₃ was used as a dry etching gas.

Then, using the resist pattern 50 a and the tantalum-based film pattern20 a as a mask, the chromium-based etching mask film 10 was dry-etched,thereby forming a chromium-based etching mask film pattern 10 a (FIG.4D). In this event, a mixed gas of Cl₂ and O₂ (Cl₂:O₂=4:1) was used as adry etching gas.

Then, as shown in FIG. 4E, the resist pattern 50 a that becameunnecessary was stripped and then a chemically amplified positive resist51 for electron beam lithography (exposure) (FEP171: manufactured byFUJIFILM Electronic Materials Co., Ltd.) was applied again to athickness of 150 nm by the spin-coating method.

Then, using the electron beam lithography apparatus, pattern writing wasperformed on the resist film 51 and, thereafter, development was carriedout using the predetermined developer, thereby forming a resist pattern51 a (FIG. 4F). Herein, the resist pattern 51 a was formed for thepurpose of forming a light-shielding band in the peripheral region ofthe substrate and forming a large-area patch pattern of alight-shielding portion or a zebra pattern for controllingtransmittance.

Then, using the chromium-based etching mask film pattern 10 a as a mask,the light-transmitting substrate 1 was dry-etched with a CHF₃ gas,thereby obtaining a phase shift pattern (phase shift portion) of thesubstrate dug-down type (FIG. 4G). In this event, the light-transmittingsubstrate 1 was etched to a depth adapted to obtain a phase differenceof 180° for ArF exposure light (193 nm) (specifically, a depth of 170nm), thereby forming a dug-down part la on the light-transmittingsubstrate 1 to provide the phase shift pattern (phase shift portion).During this dry etching, the tantalum-based film pattern 20 a (tantalumnitride (TaN) layer pattern 21 a/tantalum oxide (TaO) layer pattern 22a) gradually disappeared by the dry etching and, at the completion ofthe etching of the light-transmitting substrate 1, the TaO/TaN film at aportion with no resist pattern 51 a fully disappeared (FIG. 4G). This isbecause the etching depth 170 nm of the light-transmitting substrate 1is sufficiently large with respect to the total thickness 34 nm of theTaO/TaN film and thus the etching time is sufficiently long.

Then, the etching mask film pattern 10 a at a portion with no resistpattern 51 a was stripped by dry etching with a mixed gas of Cl₂ and O₂(Cl₂:O₂=4:1) (FIG. 4H).

Then, the resist pattern 51 a was stripped (FIG. 4I) and then cleaningwas carried out, thereby obtaining a photomask 100.

[Evaluation]

The photomask obtained in Example 1 was evaluated.

As a result, with respect to the resolution of the phase shift pattern(phase shift portion) of the substrate dug-down type formed on thephotomask, it was possible to resolve a phase shift pattern of 50 nm.

Simultaneously, the transmittance for ArF exposure light was 0.1% at thelight-shielding portion formed by the chromium-based etching mask film10 and the tantalum-based film 20 stacked together and it was possibleto achieve an optical density OD=3.0.

In the manufacturing processes of the photomask of Example 1, the resistpattern 50 a was stripped after forming the etching mask film pattern 10a (between the processes of FIGS. 4D and 4E). However, the resistpattern 50 a may be stripped after forming the tantalum-based filmpattern 20 a (between the processes of FIGS. 4C and 4D). The processingaccuracy is further improved.

In the configuration shown in FIG. 4G of Example 1, there is obtained aphotomask similar to the so-called zebra type, wherein the phase shiftpattern of the substrate dug-down type has the etching mask film pattern10 a made of the chromium-based light-shielding material. However, inthis case, the optical density of the etching mask film pattern 10 amade of the chromium-based light-shielding material is less than 3.

EXAMPLE 2

Example 2 relates to a method of manufacturing a photomask blank for usein manufacturing a phase shift mask of the type having a phase shiftportion configured by forming a dug-down part on a substrate and furtherrelates to a method of manufacturing the photomask. As compared withExample 1, Example 2 differs in the film forming conditions of atantalum nitride (TaN) layer 21, the thickness thereof, and an etchinggas used in etching thereof.

[Manufacture of Photomask Blank]

Referring to FIGS. 5A to 5J, description will be given of photomaskblank and photomask manufacturing methods according to Example 2 of thisinvention.

First, a substrate made of quartz was mirror-polished and then cleaned,thereby obtaining a light-transmitting substrate 1 of 6 inches×6inches×0.25 inches (FIG. 5A).

Then, using a DC magnetron sputtering apparatus, an etching mask film 10was formed on the light-transmitting substrate 1 (FIG. 5A).Specifically, using a chromium target, CrOCN was formed to a thicknessof 20 nm under the conditions of introducing gases and flow rates ofAr=18 sccm, CO₂=18 sccm, N₂=10 sccm and a sputtering power of 1.7 kW. Inthis event, the film stress of the CrOCN film was adjusted to be assmall as possible (preferably, substantially zero).

Then, the substrate 1 formed with the etching mask film 10 wasintroduced into a DC magnetron sputtering apparatus. After the inside ofthe sputtering apparatus was evacuated to 2×10⁻⁵ (Pa) or less, a mixedgas of Xe and N₂ was introduced into the sputtering apparatus. In thisevent, the flow rate of Xe and the flow rate of N₂ were adjusted to 12.9sccm and 5 sccm, respectively. Ta was used as a sputtering target. Afterthe gas flow rates were stabilized, the power of a DC power supply wasset to 1.5 kW, thereby forming a tantalum nitride (TaN) layer 21 havinga thickness of 23 nm on the etching mask film 10 (FIG. 5A).

Then, while the substrate 1 formed with the tantalum nitride (TaN) layer21 was maintained in the sputtering apparatus, a mixed gas containing anAr gas at a flow rate of 90 sccm and an O₂ gas at a flow rate of 34.7sccm was introduced into the sputtering apparatus and then the power ofthe DC power supply was set to 0.7 kW, thereby stacking a tantalum oxide(TaO) layer 22 having a thickness of 10 nm on the tantalum nitride (TaN)layer 21 (FIG. 5A).

In the manner described above, there was formed a tantalum-basedlight-shielding film 20 comprising the tantalum nitride (TaN) layer 21and the tantalum oxide (TaO) layer 22 stacked together.

The reflectance (front-surface reflectance) of a surface, remote fromthe substrate 1, of the light-shielding film 20 thus formed was 25.3%for ArF exposure light (wavelength: 193 nm). Further, the transmittancefor ArF exposure light was 0.1%. AES (Auger electron spectroscopy)analysis was performed, wherein the N content of the tantalum nitride(TaN) layer 21 was 15at % and the O content of the tantalum oxide (TaO)layer 22 was 65at %.

The sheet resistance was measured for the sample at the stage where thetantalum oxide (TaO) layer 22 was formed, and it was 90 Ω/square.

[Manufacture of Photomask]

As shown in FIG. 5A, using a photomask blank thus manufactured, achemically amplified positive resist 50 for electron beam lithography(exposure) (FEP171: manufactured by FUJIFILM Electronic Materials Co.,Ltd.) was applied to a thickness of 150 nm on the tantalum oxide (TaO)layer 22 by a spin-coating method.

Then, using an electron beam lithography apparatus, pattern writing wasperformed on the resist film 50 and, thereafter, development was carriedout using a predetermined developer, thereby forming a resist pattern 50a (FIG. 5B).

Then, using the resist pattern 50 a as a mask, the tantalum oxide (TaO)layer 22 was dry-etched with CHF₃ used as an etching gas, therebyforming a tantalum oxide (TaO) layer pattern 22 a (FIG. 5C).

Subsequently, using the resist pattern 50 a and the tantalum oxide (TaO)layer pattern 22 a as a mask, the tantalum nitride (TaN) layer 21 wasdry-etched with Cl₂ used as an etching gas, thereby forming a tantalumnitride (TaN) layer pattern 21 a (FIG. 5D).

Then, using the resist pattern 50 a and a tantalum-based film pattern 20a (tantalum nitride (TaN) layer pattern 21 a/tantalum oxide (TaO) layerpattern 22 a) as a mask, the chromium-based etching mask film 10 wasdry-etched, thereby forming a chromium-based etching mask film pattern10 a (FIG. 5E). In this event, a mixed gas of Cl₂ and O₂ (Cl₂:O₂=4:1)was used as a dry etching gas.

Then, as shown in FIG. 5F, the resist pattern 50 a that becameunnecessary was stripped and then a chemically amplified positive resist51 for electron beam lithography (exposure) (FEP171: manufactured byFUJIFILM Electronic Materials Co., Ltd.) was applied again to athickness of 150 nm by the spin-coating method.

Then, using the electron beam lithography apparatus, pattern writing wasperformed on the resist film 51 and, thereafter, development was carriedout using the predetermined developer, thereby forming a resist pattern51 a (FIG. 5G). Herein, the resist pattern 51 a is formed for thepurpose of forming a light-shielding band in the peripheral region ofthe substrate and forming a large-area patch pattern of alight-shielding portion or a zebra pattern for controllingtransmittance.

Then, using the chromium-based etching mask film pattern 10 a as a mask,the light-transmitting substrate 1 was dry-etched with a CHF₃ gas,thereby obtaining a phase shift pattern (phase shift portion) of thesubstrate dug-down type (FIG. 5H). In this event, the light-transmittingsubstrate 1 was etched to a depth adapted to obtain a phase differenceof 180° for ArF exposure light (193 nm) (specifically, a depth of 170nm), thereby forming a dug-down part 1 a on the light-transmittingsubstrate 1 to provide the phase shift pattern (phase shift portion).During this dry etching, the tantalum-based film pattern 20 a (tantalumnitride (TaN) layer pattern 21 a/tantalum oxide (TaO) layer pattern 22a) gradually disappeared by the dry etching and, at the completion ofthe etching of the light-transmitting substrate 1, the TaO/TaN film at aportion with no resist pattern 51 a fully disappeared (FIG. 5H). This isbecause the etching depth 170 nm of the light-transmitting substrate 1is sufficiently large with respect to the total thickness 33 nm of theTaO/TaN film and thus the etching time is sufficiently long.

Then, the etching mask film pattern 10 a at a portion with no resistpattern 51 a was stripped by dry etching with a mixed gas of Cl₂ and O₂(Cl₂:O₂=4:1) (FIG. 51).

Then, the resist pattern 51 a was stripped (FIG. 5J) and then cleaningwas carried out, thereby obtaining a photomask 100.

[Evaluation]

The photomask obtained in Example 2 was evaluated.

As a result, with respect to the resolution of the phase shift pattern(phase shift portion) of the substrate dug-down type formed on thephotomask, it was possible to resolve a phase shift pattern of 50 nm.

Simultaneously, the transmittance for ArF exposure light was 0.1% at thelight-shielding portion formed by the chromium-based etching mask film10 and the tantalum-based film 20 stacked together and it was possibleto achieve an optical density OD=3.0.

In the manufacturing processes of the photomask of Example 2, the resistpattern 50 a was stripped after forming the etching mask film pattern10a (between the processes of FIGS. 5E and 5F). However, the resistpattern 50 a may be stripped after forming the tantalum oxide (TaO)layer pattern 22 a (between the processes of FIGS. 5C and 5D). Theprocessing accuracy is further improved.

EXAMPLE 3

Example 3 relates to a method of manufacturing a photomask blank for usein manufacturing a phase shift mask of the type in which a substrate isnot basically dug down and a phase shift portion is formed by a halftonephase shift film, and further relates to a method of manufacturing thephotomask.

[Manufacture of Photomask Blank]

Referring to FIGS. 6A to 6I, description will be given of photomaskblank and photomask manufacturing methods according to Example 3 of thisinvention.

First, a substrate made of quartz was mirror-polished and then cleaned,thereby obtaining a light-transmitting substrate 1 of 6 inches×6inches×0.25 inches (FIG. 6A).

Then, using a mixed target of molybdenum (Mo) and silicon (Si)(Mo:Si=1:9 [at %]), reactive sputtering was carried out in a mixed gasatmosphere of argon (Ar) and nitrogen (N₂) (Ar:N₂=10:90 [vol %];pressure: 0.3 [Pa]), thereby forming a MoSiN-basedlight-semitransmitting phase shift film 30 having a thickness of 68 nmon the light-transmitting substrate 1 (FIG. 6A). In this event, thethickness of the phase shift film 30 was adjusted so as to obtain aphase difference of 180° for ArF exposure light (wavelength: 193 nm).The transmittance of the phase shift film 30 for ArF exposure light(wavelength: 193 nm) was 6%.

Then, using a DC magnetron sputtering apparatus, an etching mask film 10was formed on the phase shift film 30 (FIG. 6A). Specifically, using achromium target, CrOCN was formed to a thickness of 15 nm under theconditions of introducing gases and flow rates of Ar=18 sccm, CO₂=18sccm, N₂=10 sccm and a sputtering power of 1.7 kW. In this event, thefilm stress of the CrOCN film was adjusted to be as small as possible(preferably, substantially zero).

Then, the substrate 1 formed with the etching mask film 10 wasintroduced into a DC magnetron sputtering apparatus. After the inside ofthe sputtering apparatus was evacuated to 2×10⁻⁵ (Pa) or less, a mixedgas of Xe and N₂ was introduced into the sputtering apparatus. In thisevent, the flow rate of Xe and the flow rate of N₂ were adjusted to 12.7sccm and 5 sccm, respectively. Ta was used as a sputtering target. Afterthe gas flow rates were stabilized, the power of a DC power supply wasset to 1.5 kW, thereby forming a tantalum nitride (TaN) layer 21 havinga thickness of 10 nm on the etching mask film 10 (FIG. 6A).

Then, while the substrate 1 formed with the tantalum nitride (TaN) layer21 was maintained in the sputtering apparatus, a mixed gas containing anAr gas at a flow rate of 90 sccm and an O₂ gas at a flow rate of 34.7sccm was introduced into the sputtering apparatus and then the power ofthe DC power supply was set to 0.7 kW, thereby stacking a tantalum oxide(TaO) layer 22 having a thickness of 10 nm on the tantalum nitride (TaN)layer 21 (FIG. 6A).

In the manner described above, there was formed a tantalum-basedlight-shielding film 20 comprising the tantalum nitride (TaN) layer 21and the tantalum oxide (TaO) layer 22 stacked together.

The reflectance (front-surface reflectance) of a surface, remote fromthe substrate 1, of the light-shielding film 20 thus formed was 26.2%for ArF exposure light (wavelength: 193 nm). Further, the transmittancefor ArF exposure light was 0.1%. AES (Auger electron spectroscopy)analysis was performed, wherein the N content of the tantalum nitride(TaN) layer 21 was 23at % and the O content of the tantalum oxide (TaO)layer 22 was 65 at %.

The sheet resistance was measured for the sample at the stage where thetantalum oxide (TaO) layer 22 was formed, and it was 160 Ω/square.

[Manufacture of Photomask]

As shown in FIG. 6A, using a photomask blank thus manufactured, achemically amplified positive resist 50 for electron beam lithography(exposure) (PRL009: manufactured by FUJIFILM Electronic Materials Co.,Ltd.) was applied to a thickness of 120 nm on the tantalum oxide (TaO)layer 22 by a spin-coating method.

Then, using an electron beam lithography apparatus, pattern writing wasperformed on the resist film 50 and, thereafter, development was carriedout using a predetermined developer, thereby forming a resist pattern 50a (FIG. 6B).

Then, using the resist pattern 50 a as a mask, the tantalum-based film20 having the TaN and TaO layers stacked together was dry-etched,thereby forming a tantalum-based film pattern 20 a (tantalum nitride(TaN) layer pattern 21 a/tantalum oxide (TaO) layer pattern 22 a) (FIG.6C). In this event, CHF₃ was used as a dry etching gas.

Then, using the resist pattern 50 a and the tantalum-based film pattern20 a as a mask, the chromium-based etching mask film 10 was dry-etched,thereby forming a chromium-based etching mask film pattern 10 a (FIG.6D). In this event, a mixed gas of Cl₂ and O₂ (Cl₂:O₂=4:1) was used as adry etching gas.

Then, as shown in FIG. 6E, the resist pattern 50 a that becameunnecessary was stripped and then a chemically amplified positive resist51 for electron beam lithography (exposure) (FEP171: manufactured byFUJIFILM Electronic Materials Co., Ltd.) was applied again to athickness of 150 nm by the spin-coating method.

Then, using the electron beam lithography apparatus, pattern writing wasperformed on the resist film 51 and, thereafter, development was carriedout using a predetermined developer, thereby forming a resist pattern 51a (FIG. 6F). Herein, the resist pattern 51 a was formed at a portionwhere the light-shielding film pattern was to remain.

Then, using the chromium-based etching mask film pattern 10 a as a mask,the phase shift film 30 was dry-etched with two kinds of fluorine-basedgases, thereby forming a phase shift film pattern (phase shift portion)30 a (FIG. 6G). In this event, the dry etching was performed using amixed gas of a CHF₃ gas and a He gas until the tantalum oxide (TaO)layer pattern 22 a disappeared by the etching. After the tantalum oxide(TaO) layer pattern 22 a disappeared, the dry etching was performedusing a mixed gas of a SF₆ gas and a He gas. During the dry etching, thetantalum-based film pattern 20 a (tantalum nitride (TaN) layer pattern21 a/tantalum oxide (TaO) layer pattern 22 a) gradually disappeared bythe dry etching and, at the completion of the etching of the phase shiftfilm 30, the TaO/TaN film at a portion with no resist pattern 51 a fullydisappeared (FIG. 6G). This is because the thickness 68 nm of theMoSiN-based phase shift film 30 is sufficiently large with respect tothe total thickness 20 nm of the TaO/TaN film and thus the etching timeis sufficiently long.

Then, the etching mask film pattern 10 a at a portion with no resistpattern 51 a was stripped by dry etching with a mixed gas of Cl₂ and O₂(Cl₂:O₂=4:1) (FIG. 6H).

Then, the resist pattern 51 a was stripped (FIG. 6I) and then cleaningwas carried out, thereby obtaining a photomask 100.

[Evaluation]

The photomask obtained in Example 3 was evaluated.

As a result, with respect to the resolution of the phase shift filmpattern (phase shift portion) 30 a formed on the photomask, it waspossible to resolve a phase shift film pattern of 40 nm.

Simultaneously, the transmittance for ArF exposure light was 0.1% at thelight-shielding portion formed by the halftone phase shift film 30, thechromium-based etching mask film 10, and the tantalum-based film 20stacked together and it was possible to achieve an optical densityOD=3.0.

In the manufacturing processes of the photomask of Example 3, the resistpattern 50 a was stripped after forming the etching mask film pattern 10a (between the processes of FIGS. 6D and 6E). However, the resistpattern 50 a may be stripped after forming the tantalum-based filmpattern 20 a (between the processes of FIGS. 6C and 6D). The processingaccuracy is further improved.

EXAMPLE 4

Example 4 relates to a method of manufacturing a photomask blank for usein manufacturing a phase shift mask of the type in which a substrate isnot basically dug down and a phase shift portion is formed by a halftonephase shift film, and further relates to a method of manufacturing thephotomask. As compared with Example 3, Example 4 differs in thethickness of a tantalum nitride (TaN) layer 21 and an etching gas usedin etching thereof.

[Manufacture of Photomask Blank]

Referring to FIGS. 7A to 7J, description will be given of photomaskblank and photomask manufacturing methods according to Example 4 of thisinvention.

First, a substrate made of quartz was mirror-polished and then cleaned,thereby obtaining a light-transmitting substrate 1 of 6 inches×6inches×0.25 inches (FIG. 7A).

Then, using a mixed target of molybdenum (Mo) and silicon (Si)(Mo:Si=1:9 [at %]), reactive sputtering was carried out in a mixed gasatmosphere of argon (Ar), nitrogen (N₂), and oxygen (O₂)(Ar:N₂:O₂=10:80:10 [vol %]; pressure: 0.3 [Pa]), thereby forming aMoSiON-based light-semitransmitting phase shift film 30 having athickness of 89 nm on the light-transmitting substrate 1 (FIG. 7A). Inthis event, the thickness of the phase shift film 30 was adjusted so asto obtain a phase difference of 180° for ArF exposure light (wavelength:193 nm). The transmittance of the phase shift film 30 for ArF exposurelight (wavelength: 193 nm) was 15%.

Then, using a DC magnetron sputtering apparatus, an etching mask film 10was formed on the phase shift film 30 (FIG. 7A). Specifically, using achromium target, CrOCN was formed to a thickness of 15 nm under theconditions of introducing gases and flow rates of Ar=18 sccm, CO₂=18sccm, N₂=10 sccm and a sputtering power of 1.7 kW. In this event, thefilm stress of the CrOCN film was adjusted to be as small as possible(preferably, substantially zero).

Then, the substrate 1 formed with the etching mask film 10 wasintroduced into a DC magnetron sputtering apparatus. After the inside ofthe sputtering apparatus was evacuated to 2×10⁻⁵ (Pa) or less, a mixedgas of Xe and N₂ was introduced into the sputtering apparatus. In thisevent, the flow rate of Xe and the flow rate of N₂ were adjusted to 12.7sccm and 5 sccm, respectively. Ta was used as a sputtering target. Afterthe gas flow rates were stabilized, the power of a DC power supply wasset to 1.5 kW, thereby forming a tantalum nitride (TaN) layer 21 havinga thickness of 12 nm on the etching mask film 10 (FIG. 7A).

Then, while the substrate 1 formed with the tantalum nitride (TaN) layer21 was maintained in the sputtering apparatus, a mixed gas containing anAr gas at a flow rate of 90 sccm and an O₂ gas at a flow rate of 34.7sccm was introduced into the sputtering apparatus and then the power ofthe DC power supply was set to 0.7 kW, thereby stacking a tantalum oxide(TaO) layer 22 having a thickness of 10 nm on the tantalum nitride (TaN)layer 21 (FIG. 7A).

In the manner described above, there was formed a tantalum-basedlight-shielding film 20 comprising the tantalum nitride (TaN) layer 21and the tantalum oxide (TaO) layer 22 stacked together.

The reflectance (front-surface reflectance) of a surface, remote fromthe substrate 1, of the light-shielding film 20 thus formed was 26.2%for ArF exposure light (wavelength: 193 nm). Further, the transmittancefor ArF exposure light was 0.1%. AES (Auger electron spectroscopy)analysis was performed, wherein the N content of the tantalum nitride(TaN) layer 21 was 15 at % and the O content of the tantalum oxide (TaO)layer 22 was 65 at %.

The sheet resistance was measured for the sample at the stage where thetantalum oxide (TaO) layer 22 was formed, and it was 150 Ω/square.

[Manufacture of Photomask]

As shown in FIG. 7A, using a photomask blank thus manufactured, achemically amplified positive resist 50 for electron beam lithography(exposure) (FEP171: manufactured by FUJIFILM Electronic Materials Co.,Ltd.) was applied to a thickness of 150 nm on the tantalum oxide (TaO)layer 22 by a spin-coating method.

Then, using an electron beam lithography apparatus, pattern writing wasperformed on the resist film 50 and, thereafter, development was carriedout using a predetermined developer, thereby forming a resist pattern 50a (FIG. 7B).

Then, using the resist pattern 50 a as a mask, the tantalum oxide (TaO)layer 22 was dry-etched with CHF₃ used as an etching gas, therebyforming a tantalum oxide (TaO) layer pattern 22 a (FIG. 7C).

Subsequently, using the resist pattern 50 a and the tantalum oxide (TaO)layer pattern 22 a as a mask, the tantalum nitride (TaN) layer 21 wasdry-etched with Cl₂ used as an etching gas, thereby forming a tantalumnitride (TaN) layer pattern 21 a (FIG. 7D).

Then, using the resist pattern 50 a and a tantalum-based film pattern 20a (tantalum nitride (TaN) layer pattern 21 a/tantalum oxide (TaO) layerpattern 22 a) as a mask, the chromium-based etching mask film 10 wasdry-etched, thereby forming a chromium-based etching mask film pattern10 a (FIG. 7E). In this event, a mixed gas of Cl₂ and O₂ (Cl₂:O₂=4:1)was used as a dry etching gas.

Then, as shown in FIG. 7F, the resist pattern 50 a that becameunnecessary was stripped and then a chemically amplified positive resist51 for electron beam lithography (exposure) (FEP171: manufactured byFUJIFILM Electronic Materials Co., Ltd.) was applied again to athickness of 150 nm by the spin-coating method.

Then, using the electron beam lithography apparatus, pattern writing wasperformed on the resist film 51 and, thereafter, development was carriedout using the predetermined developer, thereby forming a resist pattern51 a (FIG. 7G). Herein, the resist pattern 51 a was formed at a portionwhere the light-shielding film pattern was to remain.

Then, using the chromium-based etching mask film pattern 10 a as a mask,the phase shift film 30 was dry-etched with a SF₆ gas, thereby forming aphase shift film pattern (phase shift portion) 30 a (FIG. 7H). Duringthis dry etching, the tantalum-based film pattern 20 a (tantalum nitride(TaN) layer pattern 21 a/tantalum oxide (TaO) layer pattern 22 a)gradually disappeared by the dry etching and, at the completion of theetching of the phase shift film 30, the TaO/TaN film at a portion withno resist pattern 51 a fully disappeared (FIG. 7H). This is because thethickness 89 nm of the MoSiON-based phase shift film 30 is sufficientlylarge with respect to the total thickness 22 nm of the TaO/TaN film andthus the etching time is sufficiently long.

Then, the etching mask film pattern 10 a at a portion with no resistpattern 51 a was stripped by dry etching with a mixed gas of Cl₂ and O₂(Cl₂:O₂=4:1) (FIG. 71).

Then, the resist pattern 51 a was stripped (FIG. 7J) and then cleaningwas carried out, thereby obtaining a photomask 100.

[Evaluation]

The photomask obtained in Example 4 was evaluated.

As a result, with respect to the resolution of the phase shift filmpattern (phase shift portion) 30 a formed on the photomask, it waspossible to resolve a phase shift film pattern of 50 nm.

Simultaneously, the transmittance for ArF exposure light was 0.1% at thelight-shielding portion formed by the halftone phase shift film 30, thechromium-based etching mask film 10, and the tantalum-based film 20stacked together and it was possible to achieve an optical densityOD=3.0.

In the manufacturing processes of the photomask of Example 4, the resistpattern 50 a was stripped after forming the etching mask film pattern 10a (between the processes of FIGS. 7E and 7F). However, the resistpattern 50 a may be stripped after forming the tantalum oxide (TaO)layer pattern 22 a (between the processes of FIGS. 7C and 7D). Theprocessing accuracy is further improved.

(Chemical Resistance Test)

Resistances of a TaO film, a TaN film, and a MoSiON film to hot waterand alkali (ammonia-hydrogen peroxide mixture) were examined.

The TaN film was formed on a substrate in the same manner as inExample 1. Specifically, using a Ta target, the TaN film having athickness of 50 nm was formed on a synthetic quartz substrate byreactive sputtering under the conditions where the flow rate of Xe andthe flow rate of N₂ were set to 12.7 sccm and 10 sccm, respectively, andthe power of a DC power supply was set to 1.5 kW.

The TaO film was formed on a substrate in the same manner as inExample 1. Specifically, using a Ta target, the TaO film having athickness of 50 nm was formed on a synthetic quartz substrate byreactive sputtering under the conditions where the flow rate of Ar andthe flow rate of O₂ were set to 90 sccm and 34.7 sccm, respectively, andthe power of a DC power supply was set to 0.7 kW.

The MoSiON film having a thickness of 50 nm was formed on a syntheticquartz substrate by reactive sputtering using a mixed target ofmolybdenum (Mo) and silicon (Si) (Mo:Si=1:9 [at %]) in a mixed gasatmosphere of argon (Ar), nitrogen (N₂), and oxygen (O₂)(Ar:N₂:O₂=10:80:10 [vol %]; pressure: 0.3 [Pa]).

The conditions of chemical resistance tests are shown below.

(1) Conditions of Alkali (Ammonia-Hydrogen Peroxide Mixture)

Resistance Test

-   Used Chemical Solutions: aqueous ammonia (NH₄OH)    -   29% EL grade (manufactured by Kanto Chemical Co., Inc.)    -   aqueous hydrogen peroxide (H₂O₂)    -   30% EL grade (manufactured by Kanto Chemical Co., Inc.)-   Chemical Solution Mixing Ratio:

NH₄OH:H₂O₂:H₂O=1:1:5 (volume ratio)

-   Treatment Time: immersion for 60 minutes in the above mixed chemical    solution

(2) Conditions of Hot Water Resistance Test

-   Pure Water Temperature: 90° C.-   Treatment Time: immersion for 60 minutes

The results of the chemical resistance tests are shown in Table 1 below.

TABLE 1 Thickness Change by Thickness Change by Film Alkali ImmersionHot Water Immersion Material (nm) (nm) MoSiON −1.4 −7.6 TaN −0.6 +0.8TaO +0.3 −0.5 (+ represents an increase in thickness)

For example, MoSiON being an antireflection layer in a MoSi-basedlight-shielding film (e.g. MoSi main light-shielding layer/MoSiONantireflection layer) described in Patent Document 1 or 2 isinsufficient in resistance to hot water and alkali so that a leveldifference occurs in a pattern of the MoSi-based light-shielding film.

In each Example of this invention, Ta oxide is used as theantireflection layer and is excellent in resistance to hot water andalkali as compared with MoSiON.

Comparative Example 1

In the case of using a phase shift mask blank of light-transmittingsubstrate/MoSi-based halftone phase shift film/Cr-based light-shieldingfilm/EB resist or in the case of using a photomask blank oflight-transmitting substrate/Cr-based light-shielding film/EB resist formanufacturing a phase shift mask of the substrate dug-down type, thecombination of Cr-based light-shielding film/EB resist is included andthe EB resist is etched to some degree with a mixed gas of a chlorinegas and an oxygen gas being an etching gas for the Cr-basedlight-shielding film, and therefore, it is difficult to reduce thethickness of the EB resist to 200 nm or less.

On the other hand, in this invention, the combination of tantalum-basedfilm/EB resist is employed and the EB resist has resistance to afluorine-based gas being an etching gas for the tantalum-based film, andtherefore, it is possible to reduce the thickness of the EB resist to200 nm or less. Simultaneously, with the structure of Cr-based etchingmask film/tantalum-based film, it is possible to reduce the thickness ofthe EB resist while maintaining the optical density (OD) of thelight-shielding portion (light-shielding film).

Comparative Example 2

In the case of using a phase shift mask blank of light-transmittingsubstrate/MoSi-based halftone phase shift film/Ta-based light-shieldingfilm (e.g. TaN/TaO)/EB resist or in the case of using a photomask blankof light-transmitting substrate/Ta-based light-shielding film (e.g.TaN/TaO)/EB resist for manufacturing a phase shift mask of the substratedug-down type, since the Ta-based light-shielding film (e.g. TaN/TaO) isetched with a fluorine-based gas, it cannot serve as an etching mask(hard mask) for the MoSi-based halftone phase shift film or thelight-transmitting substrate that is also etched with a fluorine-basedgas.

On the other hand, in this invention, the Cr-based film is inserted andfunctions as an etching mask (hard mask) for the MoSi-based halftonephase shift film or the light-transmitting substrate.

Comparative Example 3

In the case of using a phase shift mask blank of light-transmittingsubstrate/MoSi-based halftone phase shift film/Ta-based light-shieldingfilm (e.g. TaHf or TaZr/TaO)/EB resist or in the case of using aphotomask blank of light-transmitting substrate/Ta-based light-shieldingfilm (e.g. TaHf or TaZr/TaO)/EB resist for manufacturing a phase shiftmask of the substrate dug-down type, although a hard mask functionagainst etching with a fluorine-based gas is provided by adding Hf or Zrto Ta, when removing TaHf, damage to the MoSi-based halftone phase shiftfilm or the light-transmitting substrate cannot be avoided.

Specifically, when removing TaHf by dry etching, the TaHf metal can beetched with a Cl₂ gas, but is easily oxidized in the air, and therefore,it cannot be removed unless the physical etching effect is intensified.

On the other hand, when removing TaHf by wet etching, it is necessary touse hydrofluoric acid or hot caustic soda and thus damage to thelight-transmitting substrate or the MoSiON halftone film cannot beavoided.

In this invention, the Ta-based thin film is removed during etching witha fluorine-based gas for forming a phase shift pattern from theMoSi-based halftone phase shift film or the light-transmitting substrateand the remaining Cr-based film can be dry-etched with Cl₂+O₂ orwet-etched with ceric ammonium nitrate or the like, and therefore,damage to the phase shift pattern can be avoided.

EXAMPLE 5

Example 5 relates to a method of manufacturing a photomask blank for usein manufacturing a phase shift mask of the type in which ahigh-transmittance phase shift portion is formed by providing a halftonephase shift film and further by digging down a substrate, and furtherrelates to a method of manufacturing the photomask.

[Manufacture of Photomask Blank]

Referring to FIGS. 8A to 8J, description will be given of photomaskblank and photomask manufacturing methods according to Example 5 of thisinvention.

First, a substrate made of quartz was mirror-polished and then cleaned,thereby obtaining a light-transmitting substrate 1 of 6 inches×6inches×0.25 inches (FIG. 8A).

Then, using a mixed target of molybdenum (Mo) and silicon (Si)(Mo:Si=1:9 [at %]), reactive sputtering was carried out in a mixed gasatmosphere of argon (Ar) and nitrogen (N₂) (Ar:N₂=10:90 [vol %];pressure: 0.3 [Pa]), thereby forming a MoSiN-basedlight-semitransmitting phase shift film 30 having a thickness of 30 nmon the light-transmitting substrate 1 (FIG. 8A). In this event, thetransmittance of the phase shift film 30 for ArF exposure light(wavelength: 193 nm) was 20%, i.e. a high transmittance.

Then, using a DC magnetron sputtering apparatus, an etching mask film 10was formed on the phase shift film 30 (FIG. 8A). Specifically, using achromium target, CrOCN was formed to a thickness of 20 nm under theconditions of introducing gases and flow rates of Ar=18 sccm, CO₂=18sccm, N₂=10 sccm and a sputtering power of 1.7 kW. In this event, thefilm stress of the CrOCN film was adjusted to be as small as possible(preferably, substantially zero).

Then, the substrate 1 formed with the etching mask film 10 wasintroduced into a DC magnetron sputtering apparatus. After the inside ofthe sputtering apparatus was evacuated to 2×10⁻⁵ (Pa) or less, a mixedgas of Xe and N₂ was introduced into the sputtering apparatus. In thisevent, the flow rate of Xe and the flow rate of N₂ were adjusted to 12.9sccm and 5 sccm, respectively. Ta was used as a sputtering target. Afterthe gas flow rates were stabilized, the power of a DC power supply wasset to 1.5 kW, thereby forming a tantalum nitride (TaN) layer 21 havinga thickness of 23 nm on the etching mask film 10 (FIG. 8A).

Then, while the substrate 1 formed with the tantalum nitride (TaN) layer21 was maintained in the sputtering apparatus, a mixed gas containing anAr gas at a flow rate of 90 sccm and an O₂ gas at a flow rate of 34.7sccm was introduced into the sputtering apparatus and then the power ofthe DC power supply was set to 0.7 kW, thereby stacking a tantalum oxide(TaO) layer 22 having a thickness of 10 nm on the tantalum nitride (TaN)layer 21 (FIG. 8A).

In the manner described above, there was formed a tantalum-basedlight-shielding film 20 comprising the tantalum nitride (TaN) layer 21and the tantalum oxide (TaO) layer 22 stacked together.

The reflectance (front-surface reflectance) of a surface, remote fromthe substrate 1, of the light-shielding film 20 thus formed was 25.3%for ArF exposure light (wavelength: 193 nm). Further, the transmittancefor ArF exposure light was 0.1%. AES (Auger electron spectroscopy)analysis was performed, wherein the N content of the tantalum nitride(TaN) layer 21 was 15at % and the O content of the tantalum oxide (TaO)layer 22 was 65at %.

The sheet resistance was measured for the sample at the stage where thetantalum oxide (TaO) layer 22 was formed, and it was 85 Ω/square.

[Manufacture of Photomask]

As shown in FIG. 8A, using a photomask blank thus manufactured, achemically amplified positive resist 50 for electron beam lithography(exposure) (FEP171: manufactured by FUJIFILM Electronic Materials Co.,Ltd.) was applied to a thickness of 150 nm on the tantalum oxide (TaO)layer 22 by a spin-coating method.

Then, using an electron beam lithography apparatus, pattern writing wasperformed on the resist film 50 and, thereafter, development was carriedout using a predetermined developer, thereby forming a resist pattern 50a (FIG. 8B).

Then, using the resist pattern 50 a as a mask, the tantalum oxide (TaO)layer 22 was dry-etched with CHF₃ used as an etching gas, therebyforming a tantalum oxide (TaO) layer pattern 22 a (FIG. 8C).

Subsequently, using the resist pattern 50 a and the tantalum oxide (TaO)layer pattern 22 a as a mask, the tantalum nitride (TaN) layer 21 wasdry-etched with Cl₂ used as an etching gas, thereby forming a tantalumnitride (TaN) layer pattern 21 a (FIG. 8D).

Then, using the resist pattern 50 a and a tantalum-based film pattern 20a (tantalum nitride (TaN) layer pattern 21 a/tantalum oxide (TaO) layerpattern 22 a) as a mask, the chromium-based etching mask film 10 wasdry-etched, thereby forming a chromium-based etching mask film pattern10 a (FIG. 8E). In this event, a mixed gas of Cl₂ and O₂ (Cl₂:O₂=4:1)was used as a dry etching gas.

Then, as shown in FIG. 8F, the resist pattern 50 a that becameunnecessary was stripped and then a chemically amplified positive resist51 for electron beam lithography (exposure) (FEP171: manufactured byFUJIFILM Electronic Materials Co., Ltd.) was applied again to athickness of 150 nm by the spin-coating method.

Then, using the electron beam lithography apparatus, pattern writing wasperformed on the resist film 51 and, thereafter, development was carriedout using the predetermined developer, thereby forming a resist pattern51 a (FIG. 8G). Herein, the resist pattern 51 a was formed at a portionwhere the light-shielding film pattern was to remain.

Then, using the chromium-based etching mask film pattern 10 a as a mask,the halftone phase shift film 30 and the light-transmitting substrate 1were dry-etched in order using a CHF₃ gas, thereby forming a halftonephase shift film pattern 30 a and a dug-down part la on thelight-transmitting substrate 1 to obtain a phase shift pattern (phaseshift portion) (FIG. 8H). In this event, the light-transmittingsubstrate 1 was etched to a depth adapted to obtain a phase differenceof 180° as the sum of phase differences produced by the halftone phaseshift film pattern 30 a and the substrate dug-down part 1 a(specifically, a depth of 96 nm).

During this dry etching, the tantalum-based film pattern 20 a (tantalumnitride (TaN) layer pattern 21 a/tantalum oxide (TaO) layer pattern 22a) gradually disappeared by the dry etching and, at the completion ofthe etching of the light-transmitting substrate 1, the TaO/TaN film at aportion with no resist pattern 51 a fully disappeared (FIG. 8H). This isbecause the sum of the thickness 30 nm of the halftone phase shift film30 and the etching depth 96 nm of the light-transmitting substrate 1,being 126 nm, is sufficiently large with respect to the total thickness33 nm of the TaO/TaN film and thus the etching time is sufficientlylong.

Then, the etching mask film pattern 10 a at a portion with no resistpattern 51 a was stripped by dry etching with a mixed gas of Cl₂ and O₂(Cl₂:O₂=4:1) (FIG. 81).

Then, the resist pattern 51 a was stripped (FIG. 8J) and then cleaningwas carried out, thereby obtaining a photomask 100.

[Evaluation]

The photomask obtained in Example 5 was evaluated.

As a result, with respect to the resolution of the high-transmittancephase shift portion formed on the photomask by providing the halftonephase shift film and further by digging down the substrate, it waspossible to resolve a phase shift portion of 50 nm.

Simultaneously, the transmittance for ArF exposure light was 0.1% at thelight-shielding portion formed by the halftone phase shift film 30, thechromium-based etching mask film 10, and the tantalum-based film 20stacked together and it was possible to achieve an optical densityOD=3.0.

In the manufacturing processes of the photomask of Example 5, the resistpattern 50 a was stripped after forming the etching mask film pattern 10a (between the processes of FIGS. 8E and 8F). However, the resistpattern 50 a may be stripped after forming the tantalum oxide (TaO)layer pattern 22 a (between the processes of FIGS. 8C and 8D). Theprocessing accuracy is further improved.

Further, in the manufacturing processes of the photomask of Example 5,the tantalum oxide (TaO) layer pattern 22 a was formed using CHF₃ as anetching gas and then the tantalum nitride (TaN) layer pattern 21 a wasformed using Cl₂ as an etching gas, but instead, the tantalum oxide(TaO) layer pattern 22 a and the tantalum nitride (TaN) layer pattern 21a may be continuously formed using CHF₃ as an etching gas.

EXAMPLE 6

Example 6 relates to a method of manufacturing a photomask blank for usein manufacturing a phase shift mask of the type in which a substrate isnot dug down and a high-transmittance phase shift portion film patternis formed by providing a high-transmittance halftone phase shift film,and further relates to a method of manufacturing the photomask.

[Manufacture of Photomask Blank]

As shown in FIG. 9A, using a synthetic quartz substrate of 6 inches×6inches×0.25 inches as a light-transmitting substrate 1, there wasformed, on the light-transmitting substrate 1, a high-transmittancehalftone phase shift film 30 in the form of a laminated film comprisinga transmittance adjusting layer 31 made of TaHf and a phase adjustinglayer 32 made of SiON. Specifically, using a target of Ta:Hf=80:20 (at %ratio) and using Ar as a sputtering gas, the layer 31 made of tantalumand hafnium (TaHf layer: at % ratio of Ta and Hf in the layer was about80:20) was formed to a thickness of 8 nm and, then, using a Si target,reactive sputtering was carried out in a mixed gas atmosphere of argon(Ar), nitrogen (N₂), and oxygen (O₂) (Ar:N₂:O₂=20:57:23 [vol %]),thereby forming the SiON layer 32 having a thickness of 83 nm. In thisevent, the thicknesses of the respective layers were adjusted to causethe halftone phase shift film 30 to produce a phase difference of 180°for ArF exposure light (wavelength: 193 nm). The transmittance of thehalftone phase shift film 30 for ArF exposure light (wavelength: 193 nm)was 20%, i.e. a high transmittance.

Then, using a DC magnetron sputtering apparatus, an etching mask film 10was formed on the phase shift film 30 (FIG. 9A). Specifically, using achromium target, CrOCN was formed to a thickness of 15 nm under theconditions of introducing gases and flow rates of Ar=18 sccm, CO₂=18sccm, N₂=10 sccm and a sputtering power of 1.7 kW. In this event, thefilm stress of the CrOCN film was adjusted to be as small as possible(preferably, substantially zero).

Then, the substrate 1 formed with the etching mask film 10 wasintroduced into a DC magnetron sputtering apparatus. After the inside ofthe sputtering apparatus was evacuated to 2×10⁻⁵ (Pa) or less, a mixedgas of Xe and N₂ was introduced into the sputtering apparatus. In thisevent, the flow rate of Xe and the flow rate of N₂ were adjusted to 12.7sccm and 10 sccm, respectively. Ta was used as a sputtering target.After the gas flow rates were stabilized, the power of a DC power supplywas set to 1.5 kW, thereby forming a tantalum nitride (TaN) layer 21having a thickness of 14 nm on the etching mask film 10 (FIG. 9A).

Then, while the substrate 1 formed with the tantalum nitride (TaN) layer21 was maintained in the sputtering apparatus, a mixed gas containing anAr gas at a flow rate of 90 sccm and an O₂ gas at a flow rate of 34.7sccm was introduced into the sputtering apparatus and then the power ofthe DC power supply was set to 0.7 kW, thereby stacking a tantalum oxide(TaO) layer 22 having a thickness of 10 nm on the tantalum nitride (TaN)layer 21 (FIG. 9A).

In the manner described above, there was formed a tantalum-basedlight-shielding film 20 comprising the tantalum nitride (TaN) layer 21and the tantalum oxide (TaO) layer 22 stacked together.

The reflectance (front-surface reflectance) of a surface, remote fromthe substrate 1, of the light-shielding film 20 thus formed was 25.9%for ArF exposure light (wavelength: 193 nm). Further, the transmittancefor ArF exposure light was 0.1%. AES (Auger electron spectroscopy)analysis was performed, wherein the N content of the tantalum nitride(TaN) layer 21 was 23at % and the O content of the tantalum oxide (TaO)layer 22 was 65at %.

The sheet resistance was measured for the sample at the stage where thetantalum oxide (TaO) layer 22 was formed, and it was 185 Ω/square.

[Manufacture of Photomask]

As shown in FIG. 9A, using a photomask blank thus manufactured, achemically amplified positive resist 50 for electron beam lithography(exposure) (FEP171: manufactured by FUJIFILM Electronic Materials Co.,Ltd.) was applied to a thickness of 150 nm on the tantalum oxide (TaO)layer 22 by a spin-coating method.

Then, using an electron beam lithography apparatus, pattern writing wasperformed on the resist film 50 and, thereafter, development was carriedout using a predetermined developer, thereby forming a resist pattern 50a (FIG. 9B).

Then, using the resist pattern 50 a as a mask, the tantalum oxide (TaO)layer 22 was dry-etched with CHF₃ used as an etching gas, therebyforming a tantalum oxide (TaO) layer pattern 22 a (FIG. 9C).

Subsequently, using the resist pattern 50 a and the tantalum oxide (TaO)layer pattern 22 a as a mask, the tantalum nitride (TaN) layer 21 wasdry-etched with Cl₂ used as an etching gas, thereby forming a tantalumnitride (TaN) layer pattern 21 a (FIG. 9D).

Then, using the resist pattern 50 a and a tantalum-based film pattern 20a (tantalum nitride (TaN) layer pattern 21 a/tantalum oxide (TaO) layerpattern 22 a) as a mask, the chromium-based etching mask film 10 wasdry-etched, thereby forming a chromium-based etching mask film pattern10 a (FIG. 9E). In this event, a mixed gas of Cl₂ and O₂ (Cl₂:O₂=4:1)was used as a dry etching gas.

Then, as shown in FIG. 9F, the resist pattern 50 a that becameunnecessary was stripped and then a chemically amplified positive resist51 for electron beam lithography (exposure) (FEP171: manufactured byFUJIFILM Electronic Materials Co., Ltd.) was applied again to athickness of 150 nm by the spin-coating method.

Then, using the electron beam lithography apparatus, pattern writing wasperformed on the resist film 51 and, thereafter, development was carriedout using the predetermined developer, thereby forming a resist pattern51 a (FIG. 9G). Herein, the resist pattern 51 a was formed at a portionwhere the light-shielding film pattern was to remain.

Then, using the chromium-based etching mask film pattern 10 a as a mask,the SiON phase adjusting layer 32 was dry-etched with a fluorine-basedgas (mixed gas of SF₆ and He) as an etching gas, thereby forming a SiONphase adjusting layer pattern 32 a (FIG. 9H). During this dry etching,the tantalum-based film pattern 20 a (tantalum nitride (TaN) layerpattern 21 a/tantalum oxide (TaO) layer pattern 22 a) graduallydisappeared by the dry etching with the fluorine-based gas and, at thecompletion of the etching of the SiON phase adjusting layer 32, theTaO/TaN film at a portion with no resist pattern 51 a fully disappeared(FIG. 9H). This is because the thickness 83 nm of the SiON phaseadjusting layer 32 is sufficiently large with respect to the totalthickness 24 nm of the TaO/TaN film and thus the etching time issufficiently long.

Then, using the chromium-based etching mask film pattern 10 a and so onas a mask, the TaHf transmittance adjusting layer 31 was dry-etched witha Cl₂ gas as an etching gas, thereby forming a TaHf transmittanceadjusting layer pattern 31 a (FIG. 9I).

Then, the chromium-based etching mask film pattern 10 a was removedusing a mixed gas of Cl₂ and O₂ (Cl₂:O₂=4:1) as an etching gas (FIG.9J).

Then, the resist pattern 51 a was stripped (FIG. 9K) and then cleaningwas carried out, thereby obtaining a photomask 100 having a phase shiftfilm pattern (phase shift portion) 30 a with the structure in which theTaHf transmittance adjusting layer pattern 31 a and the SiON phaseadjusting layer pattern 32 a were stacked together.

[Evaluation]

The photomask obtained in Example 6 was evaluated.

As a result, with respect to the resolution of the phase shift filmpattern (phase shift portion) 30 a formed on the photomask, it waspossible to resolve a phase shift film pattern of 50 nm.

Simultaneously, the transmittance for ArF exposure light was 0.1% at thelight-shielding portion formed by the halftone phase shift film 30, thechromium-based etching mask film 10, and the tantalum-based film 20stacked together and it was possible to achieve an optical densityOD=3.0.

In the manufacturing processes of the photomask of Example 6, the resistpattern 50 a was stripped after forming the etching mask film pattern 10a (between the processes of FIGS. 9E and 9F). However, the resistpattern 50 a may be stripped after forming the tantalum oxide (TaO)layer pattern 22 a (between the processes of FIGS. 9C and 9D). Theprocessing accuracy is further improved.

Further, in the manufacturing processes of the photomask of Example 6,the tantalum oxide (TaO) layer pattern 22 a was formed using CHF₃ as anetching gas and then the tantalum nitride (TaN) layer pattern 21 a wasformed using Cl₂ as an etching gas, but instead, the tantalum oxide(TaO) layer pattern 22 a and the tantalum nitride (TaN) layer pattern 21a may be continuously formed using CHF₃ as an etching gas.

While this invention has been described with reference to theembodiments and Examples, the technical scope of the invention is notlimited to the scope of the description of the above embodiments andExamples. It is obvious to a person skilled in the art that variouschanges or improvements can be added to the above embodiments andExamples. It is clear from the description in the scope of claims thatthe modes added with such changes or improvements can also be includedin the technical scope of this invention.

1. A photomask blank for manufacturing a phase shift mask having alight-transmitting substrate provided with a phase shift portion adaptedto give a predetermined phase difference to transmitted exposure light,wherein the phase shift portion is a phase shift film adapted to give apredetermined phase change amount to the transmitted exposure light, andthe photomask blank comprises: an etching mask film, on a surface of thephase shift film, that is made of a material being dry-etchable with achlorine-based gas, but not dry-etchable with a fluorine-based gas, andserves as an etching mask at least until a transfer pattern is formed inthe phase shift film by dry etching; and a light-shielding film, on asurface of the etching mask film, that is made of a material mainlycontaining tantalum and has a thickness so as to be removable during thedry etching for forming the transfer pattern in the phase shift film. 2.A photomask blank according to claim 1, wherein the light-shielding filmcomprises: a light-shielding layer mainly containing tantalum nitride;and an antireflection layer stacked on an upper surface of thelight-shielding layer and mainly containing tantalum oxide.
 3. Aphotomask blank according to claim 1 or 2, wherein the thickness of thelight-shielding film is 15 nm to 50 nm.
 4. A photomask blank accordingto claim 1 or 2, wherein the etching mask film has a thickness of 5 nmto 40 nm.
 5. A photomask blank according to claim 1 or 2, wherein theetching mask film is made of a material mainly containing one ofchromium, chromium nitride, chromium oxide, chromium oxynitride, andchromium oxycarbonitride.
 6. A photomask blank according to claim 1 or2, wherein the etching mask film is made of a material containing one ofchromium, hafnium, zirconium, and an alloy containing such an element.7. A photomask blank according to claim 1, wherein the phase shift filmis made of a material mainly containing one of molybdenum silicide,molybdenum silicide nitride, molybdenum silicide oxide, and molybdenumsilicide oxynitride.
 8. A photomask blank according to claim 1, whereinthe phase shift film comprises a phase adjusting layer made of amaterial mainly containing silicon oxide or silicon oxynitride and atransmittance adjusting layer made of a material mainly containingtantalum or a tantalum-hafnium alloy.
 9. A photomask manufactured usingthe photomask blank according to claim 1 or
 2. 10. A method ofmanufacturing a phase shift mask having a light-transmitting substrate,a phase shift pattern and a light-shielding pattern, comprising thesteps of: preparing a mask blank in which a phase shift film made of asilicon-containing film, an etching mask film made of achromium-containing material, a light-shielding film made of atantalum-containing material are stacked on the light-transmittingsubstrate in this order; dry-etching by a fluorine-based gas using aresist film having the phase shift pattern as a mask to thereby form thephase shift pattern in the light-shielding film; dry-etching by achlorine-based gas using the light-shielding film having the phase shiftpattern as a mask to thereby form the phase shift pattern in the etchingmask film; forming a resist film having the light-shielding pattern onthe light-shielding film; dry-etching by a fluorine-based gas using theetching mask film having the phase shift pattern as mask to thereby formthe phase shift pattern in the phase shift film and using the resistfilm having the light-shielding pattern a mask to thereby form thelight-shielding pattern on the light-shielding film; and dry-etching bya chlorine-based gas using the resist film having the light-shieldingpattern or the light-shielding film as a mask to thereby form thelight-shielding pattern in the etching mask film.
 11. A method ofmanufacturing a phase shift mask having a light-transmitting substrate,a phase shift pattern and a light-shielding pattern, comprising thesteps of: preparing a mask blank in which a phase shift film made of asilicon-containing film, an etching mask film made of achromium-containing material, and a light-shielding film comprising alight-shielding layer made of a material mainly containing a tantalumnitride and an antireflection layer made of a material mainly containinga tantalum oxide are stacked on the light-transmitting substrate in thisorder; dry-etching by a fluorine-based gas using a resist film havingthe phase shift pattern as a mask to thereby form the phase shiftpattern in the antireflection layer; dry-etching by a chlorine-based gascontaining no oxygen using the antireflection layer having the phaseshift pattern as a mask to thereby form the phase shift pattern in thelight-shielding layer; dry-etching by a chlorine-based gas using thelight-shielding film having the phase shift pattern as a mask to therebyform the phase shift pattern in the etching mask film; forming a resistfilm having the light-shielding pattern on the light-shielding film;dry-etching by a fluorine-based gas using the etching mask film havingthe phase shift pattern as mask to thereby form the phase shift patternin the phase shift film and using the resist film having thelight-shielding pattern as a mask to thereby form the light-shieldingpattern in the light-shielding film; and dry-etching by a chlorine-basedgas using the resist film having the light-shielding pattern or thelight-shielding film as a mask to thereby form the light-shieldingpattern in the etching mask film.
 12. A method according to claim 10 or11, wherein the thickness of the light-shielding film is 15 nm to 50 nm.13. A method according to claim 10 or 11, wherein the etching mask filmhas a thickness of 5 nm to 40 nm.
 14. A method according to claim 10 or11, wherein the etching mask film is made of a material mainlycontaining one of chromium, chromium nitride, chromium oxide, chromiumoxynitride, and chromium oxycarbonitride.
 15. A method according toclaim 10 or 11, wherein the phase shift film is made of a materialmainly containing one of molybdenum silicide, molybdenum silicidenitride, molybdenum silicide oxide, and molybdenum silicide oxynitride.16. A photomask blank for manufacturing a phase shift mask having alight-transmitting substrate provided with a phase shift portion adaptedto give a predetermined phase difference to transmitted exposure light,wherein the phase shift portion is a dug-down part that is dug down froma surface of the light-transmitting substrate to a digging depth adaptedto produce the predetermined phase difference with respect to exposurelight transmitted through the light-transmitting substrate at a portionwhere the phase shift portion is not provided, and the photomask blankcomprises: an etching mask film, on a digging-side surface of thelight-transmitting substrate, that is made of a material mainlycontaining one of chromium, chromium nitride, chromium oxide, chromiumoxynitride, and chromium oxycarbonitride, and has a thickness of 5 nm to40 nm; and a light-shielding film, on a surface of the etching maskfilm, mainly containing tantalum, and has a thickness of 15 nm to 50 nm.17. A photomask blank according to claim 16, wherein the light-shieldingfilm comprises: a light-shielding layer mainly containing tantalumnitride; and an antireflection layer stacked on an upper surface of thelight-shielding layer and mainly containing tantalum oxide.